1. Field of the Invention
The invention relates to furnace heaters. More particularly, the invention relates to a furnace for heating high pressure vessels or reactors.
2. Description of the Prior Art
It is often desirable to subject substances to high pressures over 15,000 psi and high temperatures of up to about 600.degree. C. Typically, the substance is placed into a pressure vessel type container capable of withstanding such pressure and the vessel is then heated to the desired temperature. Conventional high-pressure reactors have employed internal heaters disposed directly within the container volume and have employed integral jacket heaters disposed around the reactor vessel. Internal heaters, however, become contaminated with reaction products and are difficult to clean. Cleaning is essential to prevent contamination of subsequent reactions with which the internal heater is reused. Integral jacket heaters significantly increase the cost of each individual reactor since they are not readily transferred for use with multiple reactor vessels.
To increase the versatility and cost effectiveness of a reactor heater, the heater has been configured as a separate furnace. A selected reactor vessel can then be inserted into the furnace for heating and removed therefrom after completing the heating cycle. Conventional furnaces typically have employed heater means located within the side walls of a furnace housing or enclosure. Ordinarily, the furnace enclosure walls and heater means have been spaced a discrete distance away from the vessel to provide a clearance that facilitates placement of the vessel into the furnace. Such a configuration, however, does not provide a maximized heat transfer rate from the heater means into the vessel. Furnaces have often taken over one hour to heat a vessel to about 500.degree. C.
Conventional furnaces have generally lacked heater means for heating the bottom of the vessel. As a result, the heating of the vessel is non-uniform. The temperature difference between the middle region of the vessel and the bottom region of the vessel has been as much as 5-10 percent of the total temperature rise of the furnace above the ambient temperature. For example, for a 500.degree. C. temperature rise in the furnace, a 50.degree. C. temperature variation can exist between the bottom and middle regions of the vessel.
Conventional furnaces have also lacked a reliable temperature sensor device. Typically, a thermocouple has been connected against an outwardly facing surface of the inside wall of the furnace enclosure. Consequently, the thermocouple has been separated from the actual vessel by the wall thickness of the enclosure as well as the clearance gap which exists between the furnace wall and the vessel. As a result, there has been an inaccurate monitoring of the actual vessel temperature. In addition, the thermocouple can often become disconnected from the wall of the furnace thereby making the temperature monitoring even less accurate. Since the thermocouple is generally hidden internally, it cannot be seen to check its integrity. Therefore, temperature control in conventional furnaces has been poor and the actual temperature of the vessel can overshoot the desired temperature by as much as 100.degree. C.
Thus, conventional furnaces for heating pressure vessels, such as those described above, do not provide as rapid a heating rate as is desirable. Such furnaces have produced non-uniform heating of the vessel volume, and have had unreliable and inaccurate temperature sensor systems.